The invention relates to a nozzle in particular for the powder build-up welding or thin-layer alloying of highly-stressed metal components by means of a high-energy beam.
In laser coating and alloying, under the aspect of performing the operational steps regarding the supply of the filler metal to be applied to the workpiece and its laser beam treatment in a single operation, special importance is attached to the creation of a suitable arrangement with a good positioning facility of the laser beam and supply of the stream of powder-delivery gas.
To reduce directional dependency in laser-powder build-up welding, from the Tagungsband "Lasertechnik" BIAS/VDI--Bremen 1991, Page 442 onwards under the title "Aspekte des Laser-Spritzbeschichten" by R. Becker, C. Binroth and G. Sepold, are known several nozzle refinements with the objective of a quasi-central supply of powder. The multi-beam nozzle described there only permits a centering of the stream of powder-delivery gas with difficulty, with small differences in the flow pulses of the individual beams having a negative effect. The requirement of a very precise orientation of the partial flows, which is associated with considerable expenditure, also has a disadvantageous effect.
The centering of the stream of powder-delivery gas by means of the annular nozzle presented is not possible because of the unevenly distributed discharge of powder caused by the construction. The third refinement, in which an additional separate stream of gas deviates the stream of powder downwards towards the substrate, in fact guarantees a circular distribution of the powder, but is very sensitive to dirt accumulation. The powder particles become attached to the walls of the outlet apertures and result in disruptive turbulence in the gas stream and can completely clog the nozzle aperture.
The laser spray nozzle known from U.S. Pat. No. 4,724,299 consists of a nozzle body having a first and a second sealed-off part and a beam passage, which extends between them so that the laser beam enters into the passage, passes through the first part and exits through the second part. A housing encloses the second part so that an annular passage is formed and with the said beam passage a coaxial aperture is enclosed, which allows the laser to pass. There are also means which operate with this aperture so as to convey a powder so that this and the beam coincide at a common point.
From U.S. Pat. No. 4,804,815 discloses a nozzle similar to the solution described above, which also operates according to the principle of laser spray coating and which is used for the preventative surface treatment of nickel alloys.
As a result of their special use for the laser spray coating, the two nozzle constructions mentioned have the common failing that the consumption of scavenging gas, which sprays the molten particles on to the surface to be coated, is very high. The thermal stress on the structures at the powder outlet aperture is comparatively high, as the powder particles still coincide with the laser beam inside the nozzle and thus, the melting of the powder particles occurs in the nozzle and thermal radiation occurring directly stresses the spray nozzle outlet apertures. The necessary cooling circulation of the first nozzle increases the manufacturing costs.
Therefore the object of the invention is, with the removal of the above-mentioned shortcomings and contrary to the conventional methods of laser spray coating, to create a nozzle, in particular for the laser-powder build-up welding or thin-layer alloying, which guarantees a directionally independent coating of highly-stressed metal components with the regular, annular distribution of the flow of powder material and inert gas supplied. It will be possible to connect the nozzle, as an important addition to the selection of tools already available, with few manipulations to commercially available high-performance laser installations, for example.